Soy protein and muscle gains compared with animal protein in people
What it found
People who took soy protein while weight training gained about the same strength and lean tissue as those taking whey or other animal proteins.
This was seen across nine trials involving 266 adults.
What they found
Studies in people
Strength gains
Both soy protein and whey protein led to clear increases in bench press and squat strength. There was no difference between the two groups.
Lean body mass
When all nine studies were combined, both the soy group and the animal protein group gained lean body mass. The amount gained was about the same in both groups.
Leucine amounts
Sports nutrition guidelines suggest getting up to 3 g of leucine after exercise, which takes about 38 g of soy protein. But similar strength and lean mass gains happened even when less soy protein was used.
Studies in people and animals
Isoflavones and muscle growth
Some worry that isoflavones in soy might block muscle growth. Two mouse studies found this effect, but the mice received very high doses far above what people normally eat. In these human trials, soy protein with isoflavones worked just as well as animal protein.
What the authors conclude
- They conclude that soy protein works as well as animal protein for building strength and lean tissue during weight training.
- The authors say protein source is probably not an important factor for these gains.
- They suggest including soy protein as one option among several for meeting protein needs.
How it was done
Short-term tests show whey protein triggers more muscle building than soy, likely because it contains more leucine. The authors wanted to know whether that difference still matters over longer training periods of at least six weeks.
They combined results from nine randomised trials that lasted between 6 and 36 weeks. A total of 266 adults aged 18 to 70 did weight training at least twice a week while taking either soy protein or an animal protein such as whey, beef, milk, or dairy protein.
What it can’t tell you
- Most participants were new to weight training, so these results may not apply to highly trained athletes.
- The included studies varied widely in age, gender, and design, and some had very small numbers of people.
- Scientists do not yet know if mixing soy and dairy protein would work better than using just one type.
The paper
- Title
- No Difference Between the Effects of Supplementing With Soy Protein Versus Animal Protein on Gains in Muscle Mass and Strength in Response to Resistance Exercise
- Type
- Meta-analysis
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Cite
- Messina M, Lynch H, Dickinson JM, Reed KE (2018). No Difference Between the Effects of Supplementing With Soy Protein Versus Animal Protein on Gains in Muscle Mass and Strength in Response to Resistance Exercise. International journal of sport nutrition and exercise metabolism. doi:10.1123/ijsnem.2018-0071Free full textPubMed 29722584DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error